Antimony plating bath



ANTIMONY PLATING BATH Elmer R. Breining, Warren, and William R. Vincent,

Birmingham, Mich., assignorsto general Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Applicationpc't ober 1 6', 1953, Serial No. 386,654

4 Claims. cit zen-us This invention relates to imprdvemems in the electrodeposition of antimony and more particularly to an an proved bath and process for the deposition of smooth adherent coatings of antimony;

In many instances electrodeposits of antimony produced by prior antimony lating solutions arid processes have not only been poorly adherent andextreniely brittle, butalso have exhibited a poor surface quality and have been difficult to butt or polish.

We have now discovered that" the'aforementioned"ditfi culties can be avoided and improved electrodeposits of antimony obtained from aqueous baths containing sulfonated hydroxy aromatic compounds; nated hydroxy aromatic compoulid'scdtitain} in" addition to asulfonate radical and hydroxy' g'roiiping oiithe aromatic nucleus, at least one additional substituted grouping which is capable of complexing' dissolved metals to form five or six membered ring systems. Typical of the type of addition agents contemplated in the present invention are the compounds obtained by sulfoii'a'tiug substituted phenols, catechol, derivatives of catec'li'ol sucl i' as 35 dihydroxy toluene (orcinol), isomers of catechol such as resorcinol; trihydr'oxy phenols such sspyre allatphlb're glucinol; hydroxy aromatic carboxylic" acids such as" sali cylic acid, B-resorcylic acid hydr'o'xy aromatic aldehydes such as salicylaldehyde; S-hydroxy quinolinepand naphthols such as 1-3 or 18 dihydroiiynaphthalene'.

In certain applications, it" is seven u'StoeinpLIoy, in addition to or in lieu of the" above-men mired add certain unsulfonated compounds includihglpolyhydr'i'calcohols such as glycerol, ethylene" glycol; ropylene glycol, mannitol, sorbitol, dulcitol', erythritol, or pentaerythritol; unsulfonated sugars such as dextrose, tlevuloseor sucrose; as well as unsulfonated' sugar acids" such as gluconic mucic, and saccharic a'eias; Itwilllbe"understood, of course, that the present invention con mplates the Preferred sulfo- United States Patent p use of the aboveaddition agentsas wllas'niixtures thereof. Similarly, sodium, potassium; ammsfiium; aifiiii'e, or antimony salts of the various compounds may be used.

In general, additives of the present invention form various complex organo-metallic salts which regulate the availability of metallic ions in solution." The actual chemical and electrochemicalreactions o'c'curiing-duringnplating using the additivesof the present invention a re not clearly understood at present. "However, the following discussion, indicating sulfonate'dcatechol asa n additive, is set forth to aid in understandingthe-inveriiion.

Sulfonated catechols may beused effectively in either acid or alkaline antimony plating baths. It will befunde'r stood, of course, that in the sulfonation of'cateehol; n'io'no,

di and tri sulfonic acids are obtained, the 'am'ounts'of each" depending upon the technique ofasulfonation. Hence, in the following reactions, although a monoculfonic acid is illustrated, similar reactions occur usingdi-sulfonic'racid; tri-sulfonic acidor a mixture of these acidst The effectiveness of the sulfonated catechol i's thouglitf to depend primarilyon the complexing of antitimntous 2,817,628 Patented Dec. 24, 1957 hydroxide which, in an acid solution, is indicated as follows:

Sb(0H)a Thefollowing reactions indicate the ensuing formation of monos'ulfonated antimony c'ate'ehol com lex:

In an alkaline bath a similar series of equilibrium reactions occur as summarized in the following equation:

It will be understood, oi course, that analogous antimony complexes can be formed using other additives of the present invention. The following table summarizes by compound and corresponding formula some of the antimony complexes formedin accordance with the present invention.

Compound Formula 33383? altars-.1;::::;;:;::;;;;;;;;:::: fidi i i fi S CHzC O OH Antimonyl Thioglyeollic Acid Sb is C H2C=O CH3 S C l-CO 0 H Antimonyl Thiolactic Acid Sb lSs-o-coon Antimbnyl Thloglyoollamide masonic 01cm Ethylene Glycol; Sb-O H C linkage Propylene Glycol Sl -0H nitrite Compound Formula -C 'lrimethylene Glycol Sb-OH --C linkage Glycerine Sb-H linkage Erythritol Sb-OH -(J linkage lentaerythritol.. Sb0l1 C linkage Sorbitol.. Sb-0H C linkage Mannitol 0 Sb-OH -C linkage f Arabitol Sb-OH 0 linkage Dulcitolnur Sb-OH O linkage The following is an example of a particular antimony bath of the present invention as used in an acid medium in which the quantities are expressed in grams per liter of solution: 1

Example I Antimony fluoride 220 Sulfonated catechol 237 Potassium hydroxide 300 The above bath may be used satisfactorily within a pH range from about 1 to 5, the upper pH limit generally being that at which precipitation of antimony or neutralized salts occurs. It is preferred to operate the bath using a current density within the range of from approximatelyto25 amperes per square foot. 7 The preferred bath temperature is 120" F. although the bath may be operated at a temperature within the range from room temperature, i. e: approximately 70 F., to about 165 F.

Illustrative of an alkaline bath embodying the invention is the following in which the quantities are expressed in grams per liter of solution:

Example II Antimony fluoride 220. Crude sulfonated catechol v mixture 405 (137 grams catechol). Potassium hydroxide 420.

This bath generally may be operated at a pH of 12 or greater over a range of temperatures and at a current density within the range from about 10 to 30 amperes per square foot although at present it is preferred to operate the bath at a temperature of about 140 F. using approximately 12 amperes per square foot.

The following are examples of other antimony plating baths and preferred operating conditions in accordance with the present invention.

Example III Antimony fluoride 220 g./l. Glycerol C. P 92 cc. Ammonium hydroxide To regulate pH to 2.0. Current density 25 a. s. f. Temperature 140 F.

Example IV Antimony fluoride 220 g./l. Sorbitol g./l. Ammonium hydroxide To regulate pH to 2.0. Current density 20 a. s. f. Temperature 140 F.

Example V Antimony fluoride 220 g./l. Mannitol 124 g./l. Ammonium hydroxide To regulate pH to 2.0. Current density 30 a. s. f. Temperature 140 F.

Example VI Antimony fluoride 220 g./l. Dextrose 75 g./l. Ammonium hydroxide To regulate pH to 2.0. Current density 25 a. s. f. Temperature 135 F.

Example VII Antimony fluoride 220 g./l. Sucrose 75 g./l. Ammonium hydroxide Regulate pH to 2.0. Current density 20 a. s. f. Temperature 135 F.

Example VIII Antimony fluoride 220 g./l. Levulose g./1. Ammonium hydroxide n Regulate to 2.0 pH. Current density 20 a. s. f. Temperature 135 F.

Example IX Antimony fluoride 220 g./l. Mucic acid 20 g./l. Ammonium hydroxide To regulate pH to 2.0. Current density 20 a. s. f. Temperature 125 F.

Example X Antimony fluoride 220 g./l. Gluconic acid 10 g./l. Ammonium hydroxide To regulate pH to 3.0. Current density 20 a. s. f.

Temperature 120 F.

Example XI Antimony fluoride 220 g./l. Catechol sulfonic acid mixture 125 cc. (75 g./l. catechol). Sorbitol 75 g./l. Sodium hydroxide To regulate pH to 3.5. Current density a. s. f. Temperature 130 F.

Example XII Antimony fluoride 220 g./l.

Catechol sulfonic acid mixture 190 cc. (114 g./l. catechol). Gluconic acid g./l. Sodium hydroxide To regulate pH to 4.0. Current density 20 a. s. f. Temperature 130 F.

Example XIII Antimony fluoride 220 g./l. Catechol sulfonic acid mixture 200 cc. g./l. as catechol). Levulose 45 g./l. Potassium hydroxide To regulate pH to 4.0. Current density 20 a. s. f. Temperature F.

Example XIV Antimony fluoride 220 g./l. Catechol sulfonic acid mixture 200 cc. (120 g./l. as catechol). Dextrose 45 g./l. Potassium hydroxide To regulate pH to 3.5. Current density 20 a. s. f. Temperature 125 F.

Example XV Antimony fluoride 220 g./l. Sulfonated catechol 71 g./l. (as catechol). Gluconic acid 107 g./l. Sodium hydroxide To regulate pH to 4.0. Current density 24 a. s. f. Temperature 120 F.

Example X VI Antimony fluoride 220 g./l. Sulfonated catechol 120 g./l. (as catechol). Mucic acid 3O g./l. Sodium hydroxide To regulate pH to 4.0. Current density 24 a. s. f. Temperature 120 F.

It'will be understood, of course, that the above examples are illustrative only and that suitable pH adjustments can be made to permit operation in an alkaline medium. Moreover, the particular antimony salts employed, as Well as the particular addition agents, may be varied. Although the quantities of bath ingredients can be varied, we have found that in most instances it is desirable to employ one or more compounds of antimony in a sufficient amount to provide from about 20 to 165 grams of metallic antimony per liter of solution and an additive of the present invention in an amount generally within the range of about 20 to 300 grams per liter of solution.

Although the above examples illustrate bath compositions using antimony fluoride, it will be understood, of course, that various antimony salts may be employed such as antimony oxide, antimony sulfonate, antimony pentafluoride, antimony pentoxide, potassium meta antomonite, butyl amine antimonyl tartrate, urea antimonyl tartrate, aniline antimonyl tartrate, benzyl amine antimonyl tartrate, phenyl hydrazine antimonyl tartrate, ammonium antimonyl citrate, potassium antimonyl glycollate, potassium antimonyl citrate, sodium antimonyl citrate, antimony potassium tartrate, antimony tartrate and antimony sodium tartrate.

Similarly, instead of the sodium hydroxide or potassium hydroxide indicated in the examples, the pH may be regulated using ammonia, or organic amines, such as butyl amine, trimethylamine or ethanolamine.

In the electrodeposition of antimony, as in other plating processes, proper preparation of the surface to be coated is essential. In depositing antimony on copper we have found that it is desirable to electrolytically etch the surface to be coated from one to five minutes at about 5 amperes per square foot in a 63% by volume solution of phosphoric acid at room temperature. In depositing antimony on steel it is generally advantageous to etch the steel in nitric acid, preferably diluted 1:3.

As an example of the preparation of a plating bath embodying the invention, 890 grams of catechol were added slowly to 1500 grams of C. P. sulfuric acid while maintaining the temperature of the reaction mass within the range from 85 C. to 95 C. for two hours after the last catechol Was added. The resultant catechol sulfonic acid-sulfuric acid mixture contained approximately .60 gram of catechol per cubic centimeter of crude sulfonation mass. To complete preparation of the bath 241 cc. of the sulfonation mass was then added to an antimony fluoride solution containing grams per liter of metallic ion, the pH adjusted to about 5 using sodium hydroxide, and the resultant mixture heated to 150 F. and treated with activated carbon (3 g./l.) for 2 hours and filtered.

It is to be understood that, although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

What is claimed is:

1. An electrolytic bath consisting essentially of approximately 20-165 grams per liter of solution of metallic antimony and a complexing agent capable of complexing dissolved antimony to form a five-membered ring, wherein the ring-forming complexing agent is sulfonated catechol present in a concentration of about 20-300 grams per liter of solution.

2. The method of electroplating antimony which comprises passing electric current from an anode to a cathode through the bath of claim 1.

3. An electrolytic bath as in claim 1 in which the antimony is present in the form of antimony fluoride.

4. The method of electroplating antimony which comprises passing electric current from an anode to a cathode through the bath of claim 3.

References Cited in the file of this: patent Monthly Review American Electroplaters Society, vol. 29 (1942), p. 870.

Soderberg et al.: Plating, vol. 37 (1950)), pp. 254-259. Mathers et al.: Transactions Electrochemical Society, vol. 31 (1917), pp. 293-301. 

1. AN ELECTROLYTIC BATH CONSISTING ESSENTIALLY OF APPROXIMATELY 20-165 GRAMS PER LITER OF SOLUTION OF METALLIC ANTIMONY AND A COMPLEXING AGENT CAPABLE OF COMPLEXING DISSOLVED ANTIMONY TO FORM A FIVE-MEMBERED RING, WHEREIN THE RING-FORMING COMPLEXING AGENT SULFONATED CATECHOL PRESENT IN A CONCENTRATION OF ABOUT 20-300 GRAMS PER LITEROF SOLUTION. 